2014

Abstract : Corrosion costs are estimated to 3-4% of the Gross Domestic Products (GDP) of industrialized countries, with 40% of corrosion failures potentially caused by microorganisms. The presence and heterogeneous nature of biofilms adhered to metal surface can significantly modify the local chemistry at the metal-biofilm interface, introducing physico-chemical gradients with local surface areas of different electrochemical potentials, creating batteries (‘galvanic cells’). Metabolic activity therein can drastically influence corrosion rates, by generating metal oxides and H2S, H+ and weak acids. This influences mineralogy and electron transfer between the metal, chemical and biological processes at the metal surface. Nonetheless; the diversity, metabolic and physiological activities of associated microbial communities as well as the ecological factors and their influence in triggering accelerated corrosion are poorly understood.
To investigate the peculiarity of these microbial communities, we focused on a global marine corrosion phenomenon affecting carbon steel waterfront structures, so-called ‘Accelerated Low Water Corrosion’ (ALWC). Previous studies limited to culturing approaches indicated the likely involvement of sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB). By combining molecular, cultivation, mineralogical and microscopic tools, we showed that affected areas of a harbour structure were characterized by a higher proportion of metabolically active phylotypes affiliated to specific SRB and SOB populations, of unique spatial segregation and metabolic potential differing from non-affected areas. Correlation of mineral patterns and geochemical properties with specific phylotype-inferred metabolism suggested distinct degrees of energetic/electrons flows and acidity between different areas, which could explain differences in corrosion, underlying complex metal-microbial-mineral-environmental interplay.
Investigation of other affected harbours and microcosm experiments further indicated that specific ecophysiological traits, in particular ‘electroactivity’ associated with sulfate-reducing, sulfur-oxidizing and iron-oxidizing functions constituted the core bacterial populations associated with accelerated corrosion rates. Based on these data, we hypothesized that high concentrations of nutrients, transient organic pollution in coastal waters and the presence of macro-organisms (i.e., algae and invertebrates) are key ecological factors selecting for specialized populations promoting corrosion rates from which they benefit (energetically and/or physiologically).

Abstract : Carbon steel coupons were set in the tidal zone of a French seaport (Le Havre). The layers of corrosion products covering the coupons after 6 months, 12 months and 7 years of exposure to the marine medium were thoroughly characterized by X-ray diffraction and μ-Raman spectroscopy. The results obtained for short immersion times (6 and 12 months) reveal a general process leading mainly to magnetite Fe3O4, a typical product of atmospheric corrosion favored by wet/dry cycles, and Fe(III) oxyhydroxides FeOOH. The sulfate green rust GR(SO42-), a typical product of marine corrosion [1,2], is also identified locally on the steel surface underneath magnetite. For longer exposure times (7 years), the layer of corrosion products is rather similar to that resulting from atmospheric corrosion, i.e. made of magnetite and Fe(III) oxyhydroxides. The average corrosion rate, estimated from residual thickness measurements, is ~90 μm/yr.
Other carbon steel coupons were set in the tidal zone for 7 years with a cathodic protection applied permanently, stopped after 6 years or applied only the last year. Permanently protected steel coupons are characterized by corrosion rates (~9 μm/yr) ten times smaller than those measured for unprotected coupons. The products of the residual corrosion process, similar to those observed at the open circuit potential, form a thin layer on the steel surface under the calcareous deposit. The calcareous deposit is characterised in any case by an important proportion of brucite Mg(OH)2. Pyroaurite, a Mg(II)-Fe(III) hydroxycarbonate, is also frequently identified. This compound, formed from Mg2+ and Fe3+ cations, may be considered as a result of the residual corrosion of steel or as a component of the calcareous deposit as well. Stopping cathodic protection after 6 years induces a re-acceleration of the degradation, as revealed by the accumulation of the usual corrosion products. This confirms that cathodic protection has mainly a moderating effect on the kinetics of a process basically unchanged. Finally, the delayed application of cathodic protection to previously corroded coupons seems to induce a partial reduction of Fe(III) oxyhydroxides into magnetite.

EUROCORR 2014 Pise, Italie

2013

Abstract : Most seaports in France have reached a critical age and the decision to protect the existing carbon steel structures via cathodic protection (CP) is considered. CP would however be applied on already strongly corroded steel surfaces and it is questionable whether the polarization could induce harmful effects on the corrosion system. The residual corrosion process occurring under CP also requires investigation. This phenomenon is always neglected but it may provide information to assess the efficiency of the electrochemical protection. To address these questions, carbon steel coupons were exposed to seawater in two French harbors for 5 years before to be subjected to CP for one year. The composition of the resulting rust layer was compared to that of coupons left 6 years without protection in seawater and to that of coupons maintained 6 years under cathodic protection. The layers were characterised by X-ray diffraction and μ-Raman spectroscopy and the average corrosion rates were estimated by measurements of the residual thickness of the coupons.
The application of cathodic polarization to the previously unprotected coupons induced the transformation of GR(SO42-) into GR(CO32-). GR(SO42-) is one of the main corrosion product formed on steel in seawater [1,2] and its transformation under CP may affect the mechanical integrity of the rust layer and, by releasing sulfate ions, may promote the development of sulfate-reducing bacteria. This does not imply that CP could be ineffective but it may have some impact on the residual corrosion rate.
A thin film of green rust and mackinawite was observed on the surface of the coupons permanently protected by cathodic protection during the 6 years immersion. This film was covered by a thicker layer of calcareous deposits. This result confirms that the residual anodic component of the overall current flowing through the cathodically polarized structure, usually neglected, induces the formation of various “corrosion products” underneath the calcareous deposits, as observed previously [3]. CP decreases the corrosion rate but the resulting products are basically unchanged. The study of this “residual corrosion” process may provide information allowing quantifying the effectiveness of CP.

Abstract : Here is reported investigation aimed to elucidate relationship between accelerated marine corrosion of carbon steel and community structure of bacterial biofilms associated with corrosion products. The study was conducted in three different French coastal regions (English Channel, Atlantic Ocean and Mediterranean Sea). SEM-EDX, ICP-AES, XRD and micro-Raman spectrometry revealed stratification of corrosion products based on iron oxidation state, regardless of geographical location. Molecular biology techniques and standard cultivation methods demonstrated that bacteria in corrosion products were abundant and highly diverse. Moreover, corrosion products contained many species of diatoms and multicellular organisms. Characterisation of cultivable bacteria and culture-independent molecular fingerprinting method (CE-SSCP) revealed more than 20 bacterial ribotypes in the deposits. Molecular detection of sulphate-reducing bacteria (SRB) was carried out using dissimilatory sulfite-reductase gene (dsrAB) and 16S rDNA probes specific for six SRB sub-groups. The results of microbiological analysis demonstrated that the composition and diversity of bacterial populations associated with corrosion products are determined by the chemistry of different regions, i.e. steel surface, corrosion product surface and green rust / oxy-hydroxide interface, without clear stratification. Moreover, the study confirmed that, irrespective of the site investigated, bacterial species detected in corrosion products differed from the ones present in bulk water, thus emphasising the importance of biofilm sampling when investigating corrosion failures. In view of the obtained results, the role of green rust as sulphate reservoir, the localised acidification induced by biogenically produced sulphur, the plausible role of extracellular polymeric substances in connecting bacterial cells and mineral corrosion products and the impact of multicellular organisms on the corrosion product stability are discussed.

14th International Congress on Marine Corrosion and Fouling July 27-31, 2008 Kobe, Japan

Abstract : Investigations into chemistry and microbiology of deposits formed during marine corrosion processes on surfaces of carbon steel are scarce. During the last decade a small number of in situ studies, mainly related to accelerate corrosion reported in harbour environments, has been carried out in Europe, Australia and Asia. Specific corrosion products, such as iron-sulphides in black liquid localized in the internal layer (steel side) or magnetite and iron oxy-hydroxides in external layer (seawater side), were found across the thickness of the deposit. However, the formation and the type of minerals, e.g. iron sulphide species and green rusts were not clearly identified. In this study, the structural organization and the composition of corrosion deposits formed on steel piling structures in three French ports in the English Channel, Atlantic Ocean and Mediterranean Sea have been determined. Spatial distribution of corrosion products did not differ between the three sites and it was strongly correlated with steel corrosion behaviour in saline electrolyte. The weight of the inorganic (mineral) fraction in corrosion products was frequently less than 50% (w/v) of the total weight; the other fraction being composed of water, organic compounds and micro-organisms. Bacterial diversity in the deposit was investigated using cultivable and molecular fingerprinting methods. High abundance and diversity was found in the three sites, with slight differences between surface and interface layers. The results indicate that corrosion deposits can be regarded as habitats with constant mineral fraction and stratification dependent on and following iron oxidation state. The composition and diversity of bacterial populations associated with corrosion products are determined by the chemistry of different regions, i.e. steel surface, deposit surface and green rust / oxy-hydroxide interface without clear stratification. The study confirmed that bacterial species detected in corrosion products differed from the ones present in bulk water, thus emphasising the importance of biofilm sampling when investigating corrosion failures.

International conference on biocorrosion of materials (Biocorys 2007), 11-14 June 2007, Paris

2006

Abstract : The degradation of iron-based materials by atmospheric corrosion is a well-know problem that may have incidence, especially for the storage of radioactive nuclear wastes. It is of importance to evaluate the damages due to this kind of corrosion within long time-periods. Atmospheric corrosion is thought to be a cycling process for which some parts of the corrosion layer may play a key role of electron acceptor during the wet periods. Studying atmospheric corrosion layers formed on ancient iron coupons provides helpful information on this phenomenon. Several indoor atmospheric corrosion layers (0-800 years old), were selected from different localizations in France. Each sample was scrapped from its iron substrate. The resulting powder was mixed with graphite in appropriate proportions and the mixture was pressed onto a stainless steel grid to constitute a composite electrode. The electrochemical responses of the different samples were recorded under galvanostatic regulation, in a nearneutral pH-buffered NaCl solution at 25°C. The E-t reduction curves allowed the determination of two characteristic parameters, Et / 2 , the potential value obtained at half the transition time, and Qt , the coulombic charge obtained at the end of the reduction. The diminution of Et / 2 and Qt with the age of the corrosion layer showed that the “reduction reactivity” decreases with time, suggesting a progressive stabilisation of the corrosion layer. In a second part of the work, we synthesised several common ferric or ferrous/ferric products (goethite, lepidocrocite, magnetite, maghemite, ferrihydrite) and compared their reduction responses (product alone or mixture of 2 or 3 products) to those of corrosion samples.

2004

Abstract : Microbiologically Influenced Corrosion (MIC) of carbon steel construction is widely observed in port environment in tidal and immersion zone. In the case of low water zone of microorganisms in the Accelerated Low Water Corrosion (ALWC) phenomena the influence has been identified. Most French laboratories, industrials and ports cooperate in research programs to study the bacterial consortia of marine biofilm on carbon steel surface. This study is conducted in laboratory for the fundamental approaches, but the applied approach is conducted through in situ tests in port environment in Atlantic Ocean, English Channel and Mediterranean Sea. This experimental system is developed for investigations in tidal and low water zone, with and without cathodic protection (permanent, after pre-colonization, with failure simulation). The research objectives are: to develop analytic methods, to estimate the most dangerous biofilm consortia, to estimate some risk factors for corrosive metabolism, and to estimate a prevention plan for port authorities.

Abstract : Cathodic protection is widely used to prevent corrosion of steel constructions exposed to seawater. This protection causes a calcareous deposit as well as a biofilm formation. The Sulphate-Reducing Bacteria (SRB) and Thiosulphate-Reducing Bacteria (TRB) are involved in the steel biodegradation phenomena in marine environment. The surface colonization by these species under cathodic protection are described particularly for the TRB and with immersion periods of over 30 days. After a brief-review, preliminary studies explain the first results of our investigation in natural seawater and carbon steel during 4 to 8 weeks experiment. We have made experiments with natural strains of SRB/TRB, with monoculture of Desulfovibrio halophilus (SRB) and Dethiosulfovibrio peptidovorans (TRB), with potential a Cathodic Protection (CP) of –900 mV/SCE and –1000 mV/SCE and without CP. These results seem indicate that the effects of CP on the sulphide-producing bacteria metabolism is the reduction of their corrosive activity.